Grinding machine



Oct. 16, 1945.

o. E. GAUD REAU ETAL GRINDING MACHINE Filed ma 20, 1943 :5 Sheets-Sheet 1 /5g 5; GA UDREAU.

HENRY M/CHELSEN.

THE/R ATTORNEY INVENTOBS Oct. 16', 1945. GAUDREAU 2,386,850

GRINDING MACHINE Filed May 20, 1943 3 sheets-sheet 2 I23 'uvvENTo/as ouvEe. s. aAua/asAu.

- HE/WEY MICHELSEN. FIG. 2

THE/R Az rola/verr Oct. 16, 1945. o'. E. GAUDREAU EIAL 2,386,850

' GRINDING MACHINE Filed May 20, 1943 s Sheets-Sheet s INVENTQBS.

OLIVE/2. E. mun/.95 u. HENRY M/cHELsE/v.

oY W

THE/R- ATTORNEY.

Patented Oct. 16, 1945 GRINDING MACHINE Oliver .EJGaudreau and Henry Michelsen,-Bristol,

Conn., assignors -to- General Motors Corporation, D'etroit, Miclt, a corporation of Delaware Application May20, 1943, Serial No.-487,688.

19 Claims.

This invention relates to grindingmachines and particularly to machines {which grind. with: an abrasive coated belt.

In the manufacture of antifriction bearingrace rings and other annular work pieces .whichiare-to be mounted against a shaft shoulder; and;particularly Where a fillet isformedrat the-juncture of the shoulder with the shaft, itiszdesirable to cut away the sharp circular edgeat theeend; of the shaft-receiving bore through. the work. piece ;so that the end. face ofnthe work. piece.:may abut against theshoulder.

It is thereforean object of -this.;inuention to. provide an improvedmachine whichxwill quickly and easily remove thecircular sharp edge-:whereta bore cuts through a planesurfacel.

Another object is .to-v provide ancimproved .ma chine which simply and effectively: chamfers the end of abore through a. workupiecerintoimerging. relation with a flat surfaceonithe work piece.

A further object resides in the provisionzzof an improved machine for grindingethe;end:;of.a-.bore; through an annular member to produce-a rounded. chamfer of predetermined. curvature. andxwhich blends with .the bore and .withafiat emi'face of.

the annular'member. a

To these ends and. also. tor improve generally upon devices of this character, the invention con.- sists in the various matters hereinafterzdeseribedand claimed. In its broaderzaspect'sy the-invem tion is not necessarily-limited to the specific construction illustrated in thesaccompanyingdrawings in which;

Figure 1 is a. front elevationof the invention Figure 2 is afragmentary elevation of one sideof the machine andincludinga schematic wiring diagram;

Figure 3 is a fragmentaryiside elevatiomof the Generally considered; awork piece, as the inner race-ring W of an antifriction. bearing, is rotatably supported -about' a vertical axis by=a=workholder or chuck lllzdrivenlby a motor' II which drivesv an abrasive coated 1belt: |2:"whose lowerlooped portion runsoVeraLpiVOted-wbelt posi-- tioning device including: pulleys carried by" a support memberlor spider I 4: th'at may be verti cally moved: and. tiltably. oscillated. Electrical control mechanism regulates the: movement of the'spider; [4 to shift theabrasive-belt intoandout: of abrading engagement with the circularedge'at the top of the bore through the workpiece; andelectric timers I E and- -l 6 are adjusted tocontrol the time of grinding as weli lasthe time of oscillation of the spider l4-so.that the abrasivebelt will grind 'azrequiredchamfer attheend ot the bore; and this chamfer is PI'BfEIEbIYyIOUHdEdinto blending relation both with" the .-bore eanct with the fiat. upper end face of: thework-pieee;

In the illustrated embodiment -the motor H (is mounted on top of awhollowr frame.-;20- provided; with ways 2| upon which; slides a vertically aad -i justable table 22'having adownwardlyextending through bore 24. An antifrictionwbearing- 26; mounted on thev table; rotatably supports: thechuck l0 whichhas azver-tical through bore 21 *COF', axial ofthe bore 24-andpreferablylarger-than the. bore through the work-.piece:W-whichisdemount ably supported COH-XlELHY Of 'the'chuckby awplu rality of adjustable tchuck jaws 28. Azsleeve exttension ofthis. chuckwplojeots through-the.bor.e 24 and protects .the bearing 2B-and other; moving parts. A motor pulley 29 :belt-drives-zawdual:v pulleydO-fastened on a shaft 32 -.which is-journalled in a housing; 33 that is. secured-to theitablei 22; and a pinion 34, secured :to thiszshaft drives, a ring-. ear 35' fastened to the chucktlfll The! housing 33 and a: hub on; thetpulley 30-: extend through'frame slots whichare ofa-sizeitoz allowfor-the required vertical adjustment-of: the :tabla: and a: suitable: idler pulley; beltatake-upz: (not shown) maintainsthebelt in proper driving eni-a easement withmtheapulleyaw: Vertical ladjusta mentof thetable 22 and-:of thexohuclc lllis enacted by rotation of a zvertical 'feedcscrew" 36 :threaded through bosses in the housing 33 and :supported: at its upperend forfreely rotatableznoneaxial. movement inaframeprojcction 31. A hand-wheat 38 turns a cross shaft 40 in framesupported-bear-. ings, and a gear-42 securedrto thisshaft drives a. gear-43 fastened to the feed screw 36 Alateral frame. extension, 45, overlying the-- chuck ID, has a. pair. of spaced guide ways..46 whichreceive a vertically movable slide 41, and a, stud 48 laterally extending out from the lower end. of this'slide, rotatably supports" arearwardly extending hub50 "of the 'oscillatable spider. I 4 which is generally T-shaped-witha cross arm'5l and a central downwardly extending leg 52 'beneaththe hub 50." The abrasive belt I 2; which-is driven by a motor-pulley, runs over pulleys 55 journalled onstuds adjustably clamped in slots 56 at the ends of the cross arm'5l,' and "the bottom'ofthe-lower' a pair of adjacent depending arms 58 that are pivoted at their upper ends on studs 59 secured to the leg 52. Adjustment of the spacing of the pulleys 51 is accomplished by locating the arms 58 in desired angular relation and securing them in position by screws BI passing through arcuate slots in these arms and threaded into the leg 52, and laterally engageable arm abutments limit the minimum spacing of the pulleys 51 as illustrated in Figures 1 and 5. The adjustment of the pulleys 55 and 51 relative to the spider I4 controls the angle of grinding engagement of the abrasive belt with the work, and the spacing of pulleys 51 is preferably so adjusted thatthe looped portion of the belt does not engage the work until the bottom of the belt run lies considerably below the work piece as illustrated in Figure 1.

A bracket 62, on the frame 28, has an upstanding arm on which is pivotally supported the lower head of a cylinder 63 that contains a piston connected to a-piston rod 64 slidable through a stuifing box in an upper head of the cylinder. The upper end of this piston rod is pivotally connected to the upper end of an arm 65 whose lower end is secured to a shaft 66 journalled in a frame projection 61, and an arm 68, fastened at one end to this shaft, has its other end pivotally connected to a link 69 journalled on the stud 48. Fluid under pressure, such as compressed air, fed from a suitable source through a supply pipe I8; is selectively directed by a reversing valve 12' through one of a pair of flexible ducts 13 and I4 intothe upper or lower ends of the cylinder 63 to control the lowering and raising of the slide 41 and spider I4 for bringing the abrasive belt I2 into and out of grinding position, and fluid exhausted from the cylinder 63 through the other duct is directed by the reversing valve out, of a pipe I5. As will be later described, the spider I4 during its vertical'movement is prevented from rocking movement and is maintained in a horizontal position. 7 r

A lever I6, pivotally connected at one end to an operating stem of the reversing valve I2, has its other end connected through a pivot link to the movable armature of a solenoid TI, and an intermediate portion of this lever, which is slotted to fit over a post, is pivotally and yieldably supported by a coiled spring 18 loosely surrounding this post. A nut and washer on the post adjustably secure the lever I6 against the spring I8. When the solenoid TI is deenergized, a spring (not shown) shifts the armature and the reversing valve stem to their illustrated positions wherein fluid pressure is directed through the duct I3 into the upper end of the cylinder 63 to raise the slide 41 to the top of its movement and to locate the abrasive belt above grinding position so that a work piece -W may be inserted in and removed from chuck supported engagement. Electric control mechanism, to be later described, energizes this solenoid to shift the reversing valve and bring the abrasive belt downwardly into grinding position as shown in Figure 1. A belt tightener, which maintains the abrasive belt in desired running tension irrespective of the position of the spider I4, has a belt engaging pulley I9 rotatably supported on the upper end of an outwardly urged arm 88 which is secured'at its lower end to a shaft 8| journalled in the frame projection 61, and apulley segment 82, fastened ,to this shaft, is urged downwardly by a cable pulled by a weight 83, the upper end of this cable being secured to the segment 82 and running in an arcuate groove in this seg- H ment.

An upwardly extending and rearwardly offset spider projection 85 (Fig. 4) overlies the hub 58 and is provided with a through slot in which is slidably received a locking bar 86 for movement radially of this hub to selectively engage within a vertical slot 81 in an arcuate plate 88 secured to a lateral projection 9801 the slide 4! or to engage within a slot 9| in the arcuate upper end of an oscillated rocker member 92 journalled on the hub 50. For clarity of illustration, Figure 5 shows the locking bar 86 midway of its movement between the slots 81 and 9I. To facilitate engagement and disengagement of the locking bar in these slots and to assure positioning of the spider I4 relative to the arcuate plate 88 or relative to the rocker member 92, the side walls of the slots are preferably tapered to receive tapered ends on the locking bar. The underside of the plate 88 and the arcuate upper end of the rocker member 92 are substantially concentric with the stud 48 and in closely spaced relation to the spider projection so that the locking bar may slide along one of these surfaces and be guided into one of the slots 81 or 9I in the event that the locking bar is not initially aligned with the slot into' which it is to be received.

A lever 94, pivotally supported intermediate of its ends on a cross pin for rocking movement in an opening through a boss 96 on the spider,

has a rounded inner head seated in a vertical slot in the locking bar 86, and the outer end of this lever is connected through a short pivot link to the vertically movable armature of a solenoid 98 fastened to the front of the spider I4. A coiled spring I88 loosely received in a vertical bore of the boss 96 is compressed between an adjustment screw I8I and the lever 94 to normally urge the armature out of the solenoid 98 and to urge the locking bar 86 downwardly for engagement in the slot 9|. A driving belt I83 from the dual pulley 38 drives a pulley I84 secured to a shaft I85 that is journalled in bearings on the frame 28, and a driver plate I86, fastened to this shaft, carries an eccentric crank pin I81 adjustably positioned in a transverse slot by a screw I88. A connecting rod I89, journalled at one end on the crank pin I81 and at its other end on a itud I I8 projecting from the rocker member 92, translates the crank pin movement to oscillation of the rocker member. The connecting rod I89 may be adjusted as to length so that with difierent crank pin adjustments the spider I4 may be tilted to the same extent each side of its central horizontal position. A suitable idler pulley belt take-up (not shown) maintains proper driving belt engagement with the pulleys 38 and I84.

In operation, current from a suitable power line II5 passes through a main switch I I1 and is selectively connected by the switch arm H8 and a contact II9 of a quick acting relay I28 to directly energize the solenoid 98, or by this switch arm and a contact I2I to put this solenoid under control of the electric timers I5 and I6. The main switch I", which normally remains closed, is only opened when the machine is to remain idle for a considerable time, or, this switch may be opened to provide an emergency stop for the machine. Prior to starting the machine, the relay I 28 is deeiiergized and current flows from the closed switch II-I through the wire II6, contact II9, switch arm H8 and wires I22, I23 to energize the solenoid 98 which acts through the lever 94 to hold the locking bar 86 seated in the slot B-I and secure the spider I4 -inits non-oscillating horizontal position of Figure 1. A switch I24, normally urged to a closed circuit position and mounted on the slide 41 above the 'arcuate plate 88, has a depending operating stem- I25 which is engaged by the topof the locking bar'86 to shift this switch to op'encircuit position only when the locking bar is seated in the slot- 8-1. The solenoid I1 and the relay I 20-, which are connected in parallel, are initially-deenergized as shown in their full line'positions of Figurefl, and fluid. pressure is. directed by the reversing valve I2 into the top ofthe cylinder 68 which results in locating the spider "in its upper position with the: abrasive belt I2-li=ft'ed out of grinding position.

A work 'piece- W is mounted in the chuck jaws 28 and the starting button I 26 is pressedt'o'close the switches of a controller switching mechanism I21 which operates in a-standard manner (not shown) to release an electrically controlled motor brake I28 and -to start the motor II, the closing of these switches being eliected-by the energizing of a magnetic switch control-coil s from wires I29 and I3]. The closing of-the starting button circuit also simultaneously startsboth timers I5 and I6 from their initial zero positions and energizes the solenoid of a time-delay relay I39 todelay the closingof-a'switch I32 until the motor, abrasive belt I2 and workpiece W have attained full speed. These timers and the solenoid of the time-delay relay are each connected across the wires I29, I 3I. When the starting button I26 is released, the circuits controlled by this button are held closed during timer control by a switcht inthe timer I6x While this timer It operates, a switch arm a, connected to a wire I36, is held in engagementw-ith a contact point connected to the wire I29. The time-delay relay is illustrated as including the tungsten lamp Tand the carbon lamp C to regulate the delay in closing switch I32; but any suitable time-delay relay may be employed. The closing of-the switch I32 simultaneously energizes the high speed relay I20 and the solenoid II from the wires I29, I3I. At this time, the solenoid II reverses the valve I2 causing azdownward feed of the spider to its bottom positiori to locatetheabrasive belt I2 in work-grinding engagement. The energizing of the relay I20 causes a sufiiciently rapid shifting of the switch arm I I8 to the contact I 2| to transfer control of the solenoid 58 tothe timers while maintaining the locking bar 86. in the slot 81. Current now flows from the wire I36 through the normally closed switch 12 of the timer I5 and through a wire I3'I to the contact point I2I, through arm H8, and Wire I22 thus placing solenoid 98 under timer control.

Each of the timers may be of a standard construction wherein a self-starting electric clock is provided with a sweep second hand I34-and an adjustable hand I35 which may be manually preset to determine when the timerswitches are to be operated. The adjustment of the timer I5 controls the grinding time before oscillation of the abrasive belt, and the timer I6 is adjusted to control the extent of theentire grinding period including the time of oscillation. In the event that no oscillation is desired, the timer I6 is presetto operate for the same periodas that of the timer I5. When oscillation is desired, after a predetermined [time dependent upon the setting of the hand I35 on timer I5, the switch 12 is opened and breaks the circuitto the solenoid 88: causing: the spring pressed lever "84' tQ Shift t1fe locking bar 86outofltheslot 851 and downwardly onto the rocker member "92 and into the slot 9| causing the spider Il'to be os-' cillated so that the belt I2 will grind-the desired chamfer curvature in the end ofthawork' bore; We 'preferably preadjust the pulleys 55 andii andiregulate the extent of spider oscillationiso thatithis chamfer' curvature: will blend both with thevboreandwith the:end' face of the workpiece. Thisoscillation continues until the. hands of tuner I 6 are I corres ondingly positioned whereuponthe. armubreaks' circuit from the contact connected with the wire I29 and momentarily makes circuit with at contact connected to the wire "I 22 causing. the :solenoid 98: to" again become energized and to shift-Ithelocking' bar 86 upwardly for engagement within its slot 81 At the completion of the timing cycle; when the timeriS-operates its switch \t, electrical 'connec tions (not shown) butstandard to timing de vices; stops thesetimers and resets them back-to their zero starting positions Whenthe armia breaks contact. from the wire: I29; 'theclosed switch I24 maintains a circuit :across thestarting button I26 through the wires. I39, -I40 and' I36 so that the relay I20, solenoid TI, and time delay switch I30 remainin theirsame energized positions, and: the controller switching m'echa nismI 21 remains in its previously shifted closed circuit positions;

The seating of the locking bar 86 within its slot 81 again secures thespiderldin itsnonoscillating horizontal position and. opens the switch I24 thereby breakingthecircuitlto the relay I20, solenoidTI, timedelay switch I30. and to the magneticswitchcontrol coil s; Thexswitch arm II.8"of thenowdeenergizedrelay I2Il:ra'pidly shifts from'conta'c't I2I to'contact H9 to transfer' the :solenoid T98 from timer control to. main powerline control with sufiicient rapidity so that the locking .bar 86 remains withinits. slot 81; The deenergized solenoid 11' returns to itsillustratedposition of Figure -2 and'allows thevalve I2'tc reverse causing an upward movement of the slide 41 andJspiderM to their'top positions to lift the abrasive belt out of grinding position. Since the switch I24 cannot be opened .until the spider I4=.is locked in its horizontal non-oscillating position, the solen'oid *I'Iwill not :be prematurely; energizedand the spider cannot be tilted whilebeing lifted outofthe work piece W with the consequent dangerofbreakage of the abrasivexbelt I2; spider I4 and work iece. The 'deenergizing'of thetime delay relay I30 returns the switch arm, I 32. toits initial open circuit :position and at the same time the deenergizing of the magneticswitch control coil s permits the controller switching mechanism I21 to return to its indicated open circuit positions, so that the motor I 'I =is'disc0nnected and the brake I 28.is applied immediately after the abrasive belt is withdrawn from grinding "position. The ground work piece W is-removed from the chuck which has now stopped rotating and the machine parts are again ready for aiduplicate operating cycle.

1; Ida device ofthe"characterindicated, a work holder forrotatably supporting a work piece havinga bore, an-abrasive belt provided with a looped portion receivable insaid bore for grinding the work piece, belt driving means, feeding mechanism'xfor feeding said looped portion into and out of grinding position, oscillating mechanism for'. producingtaarelative oscillation between said looped portion and said work pieceduringgrinding, and means preventing simultaneous opera-.- tion of the feeding mechanismand of the oscillating mechanism. j

2. In a device of the character indicated,.'a work holder for rotatablysupporting a work piece having a bore, an abrasive belt, engageable with the work piece at an edge ,of said bore, belt driving mechanism, a belt guiding device including a member receivable within said bore, feeding means to enter said member within the bore for locating a running portion of the belt against the work piece, mechanism producing a relative tiltable oscillation between the belt guiding device and the Work piece, and means preventing said oscillation during the feeding of said member into the work bore.

3. In a device of the character indicated, a work holder for rotatably supportingia work piece having a bore, an abrasive belt provided with a looped portion receivable in said bore for grinde ing the work piece, belt driving means, a pivotally mounted member, belt supporting pulleys adjustably mounted on said member for regulating the shape of said looped portion, and means for tiltably oscillating said pivotally mounted member during the grinding operation.

4. In a device of the character indicated, a work holder for rotatably supporting a work piece having a bore, an abrasive belt provided with a looped portion receivable in said bore for grinding the work piece, belt driving means, a pivotally mounted device for guiding the looped portion of the belt, mechanism for tiltably oscillating the pivotally mounted device, and means to regulate the extent of said oscillation.

5. In a device of the character indicated, a work holder for rotatably supporting a Work piece having a bore, an abrasive belt provided with a looped portion, means to drive the belt, a pivotally mounted device for positioning said.looped portion, feeding means for said pivotally mounted device to insert the looped portion into said bore to a grinding position and to withdraw the looped portion from said bore, mechanism for oscillating said pivotally mounted device during grinding, and means operated in timed relation to the feeding means for preventingsaid oscillation'during the feeding movement of the looped portion into and out of said bore.

6. In a device of the character indicated, a work holder for rotatably supporting a work piecehaving a bore, an abrasive belt provided with a looped portionreceivable in said bore,.means to drive the belt, a pivotally mounted device for positioning the looped portion of the belt, mechanism to oscillate' thepivotally mounted device, a member detachably locking the pivotally mounted device in a non-oscillating position, feeding means for producing a relative feeding movement between the pivotally mounted device and the work holder one towards and from the other,: and control mechanism for simultaneously actuating said feeding means. and for securingsaid member in its locking position. 1.

7. In a device-of the character. indicated, a work holder for rotatably supporting a work piece having a bore, an abrasive belt provided with a looped portion, means to drive the belt, a pivotal device for positioning said looped portion, mechanism to oscillate the pivotal device, feeding means for feeding said device towards and from the work holder to insert the looped portion into grinding engagement within said bore and to withdraw the looped portion from said bore, and a member selectively movedto hold said device in an intermediate non-oscillating position while said feeding means is operated and selectively moved to operatively connect said device to the oscillating mechanism during the grinding engagement of said looped portion with the work piece.

'8. In a device of the character indicated, a work holder for supporting a work piece having a bore, a slide movable towards and from the work holder, a spider pivotally mounted on said slide, spaced pulleys adjustably positioned on said spider, an abrasive belt having a looped portion positioned by said pulleys and receivable in said bore, a pivotally mounted oscillating member located coaxially of said spider and having a slot, means providing a slot fixedly positioned with respect tosaid slide, a locking bar carried by said spider and selectively engageable with said slots, feeding mechanism for said slide to insert the looped portion of the belt into said bore to a grinding position and to retract the belt from said bore, and means securing the locking bar'in said fixedly positioned slot whenever the feeding mechanism is operated.

9. In a device of the character indicated, a work holder for rotatably supporting a work piece having a, bore, a slide movable towards and from the work holder, an abrasive belt provided with a looped portion, means to drive the belt, a pivotal device positioning said looped portion and supported for tiltable oscillation on said slide, an oscillatably driven member coaxial of the pivotal device and having a slot, means on said slide providing a slot in fixed relation to said slide, a looking bar slidably mounted on the pivotal device for selective engagement with said slots, feeding mechanism for the slide to insert the looped portion, into said bore to a grinding position and to withdraw'it from said bore, and means making said feeding mechanism inoperative whenever the locking bar is withdrawn from said fixed slot.

10. In a device of the character indicated, a work holder for supporting a work piece provided with an opening, an abrasive belt having a looped portion, feeding means for inserting the looped portion into work grinding engagement Within said opening and for removing it out of work grinding engagement, and adjustable timing mechanism for said feeding means to control the time that said looped portion remains in said opening.

' 11. In a device of the character indicated, a work holder for supporting a work piece provided with a bore, an abrasive belt having a looped portion, belt driving means, feeding mechanism for inserting said looped portion to a work grinding position within said bore and for removing it from said bore, and adjustable timing means for controlling the feeding mechanism to remove the looped portion from said bore atthe end of a predetermined grinding period.

12. In a device of the character indicated, a Work holder for supporting a work piece provided with a bore, an abrasive belt having a looped portion, belt driving means, a belt guiding device for said looped portion, means for feeding the belt guiding device towards and from the work holder to insert the looped portion to a grinding position within said bore and to withdraw the looped portion from said bore, a timing mechanism for controlling the feeding means to determine the extent of time that the looped portion remains within said bore, and a control mechanism for causing the feeding means to insert said looped portion within'the bore and for placing the feeding means under subsequent control of the timing mechanism.

13. In a device of the character indicated, a work holder for rotatably supporting a work piece having a bore, an abrasive belt provided with a looped portion receivable in said bore, belt driving means, a pivotally supported device for positioning said looped portion, means for feeding the pivotally supported device towards and from the work holder to insert the looped portion into and to withdraw it from said bore, mechanism for tiltably oscillating said pivotally supported device, and adjustable timing mechanism for controlling the extent of time that said pivotally supported device is oscillated.

14. In a device of the character indicated, a work holder fo rotatably supporting a work piece provided with a bore, an abrasive belt having a looped portion receivable in said bore, belt driving means, a pivotally mounted device for positioning said looped portion, means for feeding said pivotally mounted device towards and from the work holder to insert the looped portion within said bore into work grinding engagement and to withdraw the looped portion from said bore, means to oscillate the pivotally mounted device during a portion of the time that the belt is in work grinding engagement, and adjustable timing mechanism for adjustably controlling the duration of said oscillation and for adl'ustably controlling the total grinding time.

15. In a device of the character indicated, a work holder for rotatably supporting a work piece provided with a bore, an abrasive belt having a looped portion, means to drive the belt, a pivotal device positioning said looped portion, feeding means for said pivotal device for inserting the looped portion into said bore to a grinding position and for withdrawing the looped portion from said bore, means to oscillate the pivotal device during a portion of the time the said looped portion is in grinding position, locking means preventing said oscillation during said insertion and withdrawal of the pivotal device, and adjustable timing mechanism adjustably regulating the extent of time that said looped portion remains in grinding position.

16. In a device of the character indicated, a work holder for a work piece provided with a bore, an abrasive belt having a looped portion receivable in said bore, a belt guiding device for said looped portion, belt driving means, starting mechanism for said belt driving means, feeding means for producing a relative feed between the belt guiding device and the work holder one towards and from the other for presenting the looped portion at a grinding position within said bore and for removing the looped portion from said bore, adjustable timing mechanism for controllin the operation of the feeding means which removes said looped portion from the work piece bore at the end of a predetermined time, and means responsive to the starting mechanism for controlling the operation of said feeding means which presents the looped portion within said bore and for connecting said feeding means under subsequent control of the timing mechanism.

17. In a device of the character indicated, a work holder for a work piece provided with a bore, an abrasive belt having a looped portion, a belt guiding device for said looped portion, belt driving means, starting mechanism for said driving means, feeding means to produce a relative feed between the belt guiding device and the Work holder one towards and from the other for inserting the looped portion to a grinding position within said bore and for withdrawing the looped portion from said bore, adjustable timing mechanism for controlling the operation of the feeding means which withdraws said looped portion from the bore at the end of a predetermined time, means responsive to the starting mechanism for controlling the operation of the feeding means which presents the looped portion within said bore and for connecting the feeding means under subsequent control of the timing mechanism, and mechanism under control of the starting mechanism for producing a predetermined delay in placing the feeding means under control of the starting mechanism.

18. In a device of the character indicated, a work holder for a Work piece provided with a bore, an abrasive belt having a looped portion, a belt guiding device for said looped portion, a motor for driving said belt, motor starting mechanism, feeding means for moving the belt guiding device towards and from the work holder for inserting the looped portion into said bore to a grinding position and for withdrawing the looped portion out of said bore, adjustable timing mechanism for controlling the operation of the feeding means which withdraws the looped portion out of said bore, switching mechanism responsive to the motor starting mechanism for controlling the operation of the feeding means which inserts the looped portion into said bore and for starting said timing mechanism, and means producing a predetermined delay in the operation of said switching mechanism.

19. In a device of the character indicated, a work holder for rotatably supporting a work piece provided with a bore, an abrasive belt having a looped portion, belt driving means, a pivotal device guiding said looped portion, feeding means for said device for inserting the looped portion into said bore to a grinding position and for withdrawing the looped portion from said bore, means to oscillate the pivotal device during a portion of the time that the looped portion is in grinding position, locking means preventing oscillation of the pivotal device during said insertion and withdrawal of the looped portion and during a portion of the grinding period, and adjustable timing mechanism for regulating the duration of said oscillation and for regulating the extent of total grinding time.

OLIVER E. GAUDREAU. HENRY MICHELSEN. 

